Revealing crossed-beam energy transfer as the origin of asymmetric backscattering in hohlraums

Backscattering due to laser plasma instabilities (LPIs) presents a risk in the laser-driven inertial confinement fusion. Generally, it is assumed that the backscattering of laser beams in the same cone is identical in hohlraum physics studies. In the experiments performed at SG-100kJ laser facility, we find that the backscattering of laser beams in the same cone are quite different. Our investigation reveals the main reason for this phenomenon is that the laser beams in the same cone obtain different power from their neighbor beams via crossed-beam energy transfer (CBET) depending on their polarizations. The dependence of multi-beam CBET on laser polarization arrangement is confirmed in a specially designed experiment. These findings are crucial for understanding the backscattering, CBET, energy deficit and the azimuthal drive asymmetry in cylindrical hohlraums.